During their production, single-walled carbon nanotubes form bundles. Owing to the weak van der Waals interaction that holds them together in the bundle, the tubes can easily slide on each other, resulting in a shear modulus comparable to that of graphite. This low shear modulus is also a major obstacle in the fabrication of macroscopic fibres composed of carbon nanotubes. Here, we have introduced stable links between neighbouring carbon nanotubes within bundles, using moderate electron-beam irradiation inside a transmission electron microscope. Concurrent measurements of the mechanical properties using an atomic force microscope show a 30-fold increase of the bending modulus, due to the formation of stable crosslinks that effectively eliminate sliding between the nanotubes. Crosslinks were modelled using first-principles calculations, showing that interstitial carbon atoms formed during irradiation in addition to carboxyl groups, can independently lead to bridge formation between neighbouring nanotubes.

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Optical nanoantennas have a great potential for enhancing light-matter interactions at the nanometer scale, yet fabrication accuracy and lack of scalability currently limit ultimate antenna performance and applications. In most designs, the region of maximum field localization and enhancement (i.e., hotspot) is not readily accessible to the sample because it is buried into the nanostructure. Moreover, current large-scale fabrication techniques lack reproducible geometrical control below 20 nm. Here, we describe a new nanofabrication technique that applies planarization, etch back, and template stripping to expose the excitation hotspot at the surface, providing a major improvement over conventional electron beam lithography methods. We present large flat surface arrays of in-plane nanoantennas, featuring gaps as small as 10 nm with sharp edges, excellent reproducibility and full surface accessibility of the hotspot confined region. The novel fabrication approach drastically improves the optical performance of plasmonic nanoantennas to yield giant fluorescence enhancement factors up to 10 4 −10 5 times, together with nanoscale detection volumes in the 20 zL range. The method is fully scalable and adaptable to a wide range of antenna designs. We foresee broad applications by the use of these in-plane antenna geometries ranging from large-scale ultrasensitive sensor chips to microfluidics and live cell membrane investigations. KEYWORDS: Optical nanoantennas, template stripping, electron beam lithography, fluorescence enhancement, plasmonics O ptical nanoantennas take advantage of the plasmonic response of noble metals to strongly confine light energy into nanoscale dimensions and breach the classical diffraction limit. 1−3 This confinement leads to a drastic enhancement of the interactions between a single quantum emitter and the light field, 4−7 enabling large fluorescence gains above a thousand fold, 8−13 ultrafast picosecond emission, 14−16 and photobleaching reduction. 17,18 As such, optical antennas hold great interest for ultrasensitive biosensing, especially for the detection of single molecules at biologically relevant micromolar concentrations. 19−21 Biosensing applications of nanoantennas require the largescale availability of narrow accessible gaps. Not only should nanogaps with sub-20 nm dimensions be reproducibly fabricated but also the gap region (plasmonic hotspot) must remain accessible to probe the target molecules. Despite impressive recent progress using electron beam, 22 focused ion beam, 23 or stencil lithographies 24−26 or alternatively with bottom-up self-assembly techniques, 6,7,9,13,16,27−30 the challenges of reliable narrow gap fabrication and hotspot accessibility remain major hurdles limiting the impact and performance of optical nanoantennas. For instance, when aiming for the fabrication of aperture antennas, electron beam lithography (EBL) using a positive-tone resist requires metal dry etching, which produces high line-edge roughness that are not suited for the definition ...

Nanoscale color printing has recently emerged as a unique alternative to traditional pigments by providing record spatial resolution, angular independent, durable and single material colors. Widely based on plasmonic nanostructures, numerous efforts in the field have aimed at extending color range and saturation relying on a variety of designs and metals. Alternatively, silicon nanostructures support finely tunable electric and magnetic multipolar resonances, afford low absorption losses and benefit from well-established industrial fabrication processes, all features ideally suited to nanoscale color printing. Here we compare the properties of silicon nanodiscs with those of aluminum and silver plasmonic elements for the specific purpose of nanoscale color reproduction targeting the coverage of a broad and vivid color palette. We highlight the different properties of such metallic and dielectric resonators in various geometric and illumination conditions leading to the optimization of silicon nanodisc arrays for the fabrication of high resolution color features as well as millimetric paining replicas. The fabricated structures span a large, continuous color range with varying hue and saturation that is visible by conventional optical microscopy, photography as well as the bare eye under white light illumination. High-throughput electron beam lithography as well as color mixing schemes are discussed to further harness the unique properties of silicon nanodiscs as color elements, paving the way for a broader exploitation of nanoscale color printing.

The controlled tuning of the characteristic dimensions of two‐dimensional arrays of block‐copolymer reverse micelles deposited on silicon surfaces is demonstrated. The polymer used is polystyrene‐block‐poly(2‐vinylpyridine) (91 500‐b‐105 000 g mol–1). Reverse micelles of this polymer with different aggregation numbers have been obtained from different solvents. The periodicity of the micellar array can be systematically varied by changing copolymer concentration, spin‐coating speeds, and by using solvent mixtures. The profound influence of humidity on the micellar film structure and the tuning of the film topography through control of humidity are presented. Light scattering, atomic force microscopy, scanning electron microscopy, transmission electron microscopy, and X‐ray photoelectron spectroscopy were used for characterization. As possible applications, replication of micellar array topography with polydimethylsiloxane and post‐loading of the micelles to form iron oxide nanoparticle arrays are presented.